The present invention relates generally to an antenna structure and, more particularly, to an antenna structure for use in a mobile terminal.
In PCS band full duplex systems, the duplex separation of receiving and transmitting bands is so small that it sets very stringent requirements for the duplex filters. To meet these requirements, the overall volume of the duplexer is typically very large. Consequently, the losses in the signal path are very high. Moreover, the thickness of a mobile phone equipped with such a duplexer is not easily reduced.
It is advantageous and desirable to provide an antenna structure that does not require a large volume, while the isolation in the antenna can be improved.
It is a primary object of the present invention to provide an antenna structure having a transmit antenna and a receive antenna, wherein the isolation between the transmit and receive antennas is improved. The object can be achieved by providing a cut in the ground plane for causing the conducted power in the ground plane to undergo a 180-degree phase shift with respect to the radiated power in air. Alternatively, one of the antennas is a planar inverted-F antenna (PIFA) whereas the other is a slot antenna, wherein the signal fed to the slot antenna undergoes a substantially 180-degree phase shift before it is coupled to the ground plane.
According to the first aspect of the present invention, there is provided an antenna structure (1) comprising:
a ground plane (10) having a first section (12) and a second section (14) galvanically connected to the first section (12); and
an antenna system (22, 24) operable in a frequency band disposed over the ground plane (10), the antenna system comprising a receive antenna (22) and a transmit antenna (24), wherein
the receive antenna (22) comprises a first radiating element (30) disposed over the first section (12) of the ground plane (10), and a first grounding strip (34) for grounding the first radiating element (30) to the first section (12) of the ground plane (10); and
the transmit antenna (24) comprises a second radiating element (40) disposed over the second section (14) of the ground plane (10), and a second grounding strip (44) for grounding the second radiating element (40) to the second section (14) of the ground plane (10). The antenna structure is characterized by
a slot (20) provided between the first section (12) and the second section (14) of the ground plane (10) for improving isolation between the receive antenna and the transmit antenna, wherein the slot has an effect length (L) substantially equal to a quarter wavelength of the frequency band.
According to the present invention, the first section (12) is connected to the second section (14) by a connecting section (16) of the ground plane (10) for realizing the effective length (L). Alternatively, the antenna structure further comprises a switching means (64) over the slot (20) operated in a closed position for realizing the effective length (L).
According to the present invention, the antenna structure further comprises a transceiver antenna (26) operable in a further frequency band different from the frequency band, wherein the transceiver antenna (26) comprises a third radiating element (50) disposed over the ground plane, straddling both the first and second sections of the ground plane, and a third grounding strip (54) for grounding the third radiating element to the ground plane. The antenna structure is characterized by
a switching means (60) disposed over the slot, wherein the switching means is operable
in a closed position, for electrically connecting the first section (12) and the second section (14) when the antenna structure (1) is operating in the further frequency band, and
in an open position, for keeping the first section (12) and the second section (14) electrically separated over the slot, when the antenna structure (1) is operating in the frequency band.
According to the present invention, the antenna structure further comprises a further antenna system (122, 124) operable in a third frequency band different from the frequency band, the further antenna system comprising a further receive antenna (122) and a further transmit antenna (124), wherein
the further receive antenna (122) comprises a fourth radiating element (130) disposed over the first section of the ground plane, and a fourth grounding strip (134) for grounding the fourth radiating element to first section of the ground plane; and
the further transmit antenna (124) comprises a fifth radiating element (140) disposed over the second section of the ground plane, and a fifth grounding strip (144) for grounding the fifth radiating element to the second section of the ground plane. The antenna structure is characterized in that
the switching means (60) is also operating in the open position when the antenna structure is operating in the third frequency band. The antenna structure is further characterized by
a further switching means (62, 64) disposed over the slot, wherein the further switching means is operable
in a closed position for retaining the effective length (L) of the slot when the antenna structure is operating in the frequency band, and
in an open position for realizing an effective length (Lxe2x80x2) of the slot substantially equal to a quarter wavelength of the third frequency band when the antenna structure is operating in the third frequency band.
Alternatively, the further switching means (64) is operable
in an open position for retaining the effective length (L) of the slot when the antenna structure is operating in the frequency band, and
in a closed position for realizing an effective length (Lxe2x80x2) of the slot substantially equal to a quarter wavelength of the third frequency band when the antenna structure is operating in the third frequency band.
According to the second aspect of the present invention, there is provided a method of improving isolation in an antenna structure (1), wherein the antenna structure (1) comprises:
a ground plane (10) having a first section (12) and a second section (14) galvanically connected (16) to the first section (12), and
an antenna system (22, 24) operable in a frequency band disposed over the ground plane (10), the antenna system comprising a receive antenna (22) and a transmit antenna (24), wherein
the receive antenna (22) comprises a first radiating element (30) disposed over the first section (12) of the ground plane (10), and a first grounding strip (34) for grounding the first radiating element (30) to the first section of the ground plane (10); and
the transmit antenna (24) comprises a second radiating element (40) disposed over the second section (14) of the ground plane (10), and a second grounding strip (44) for grounding the second radiating element (40) to the second section of the ground plane (10). The method is characterized by
providing a slot (20) between the first section (12) and the second section (14) of the ground plane for improving isolation between the transmit antenna and the receive antenna, wherein the slot has an effective length (L) substantially equal to a quarter wavelength of the frequency band.
According to the present invention, wherein the antenna structure (1) further comprises a transceiver antenna (26) operable in a further frequency band different from the frequency band, the transceiver antenna (26) comprising a third radiating element (50) disposed over the ground plane, straddling both the first and second sections of the ground plane, and a third grounding strip (54) for grounding the third radiating element to the ground plane. The method is further characterized by
providing a switching means (60) over the slot, wherein the switching means is operable
in a closed position, for electrically connecting the first section (12) and the second section (14) when the antenna structure (1) is operating in the further frequency band, and
in an open position, for keeping the first section (12) and the second section (14) electrically separated over the slot (20), when the antenna structure (1) is operating in the frequency band.
According to the third aspect of the present invention, there is provided by a mobile terminal (200) having an improved antenna structure (1) for receiving and transmitting information in a frequency band, the antenna structure (1) comprising:
a ground plane (10) having a first section (12) and a second section (14) galvanically connected (16) to the first section (12), and an antenna system (22, 24) disposed over the ground plane (10), the antenna system (22, 24) comprising a receive antenna (22) and a transmit antenna (24), wherein
the receive antenna (22) comprises a first radiating element (30) disposed over the first section (12) of the ground plane (10), and a first grounding strip (34) for grounding the first radiating element (30) to the first ground plane (10); and
the transmit antenna (24) comprises a second radiating element (40) disposed over the second section (14) of the ground plane (10), and a second grounding strip (44) for grounding the second radiating element (40) to the second section of the ground plane (10). The mobile terminal is characterized by
a slot (20) provided between the first section (12) and the second section (14) of the ground plane (10) for improving isolation between the receive antenna and the transmit antenna, wherein the slot has an effective length (L) substantially equal to one quarter wavelength of the frequency band.
According to the present invention, wherein the antenna structure (1) further comprises a transceiver antenna (26) operable in a further frequency band different from the frequency band, the transceiver antenna (26) comprising a third radiating (50) element disposed over the ground plane, straddling both the first and second sections of the ground plane, and a third grounding strip (54) for grounding the third radiating element to the ground plane. The mobile terminal is characterized by
a switching means (60) disposed over the slot, wherein the switching means is operable
in a closed position, for electrically connecting the first section (12) and the second section (14) when the antenna structure is operating in the further frequency band, and
in an open position, for keeping the first section (12) and the second section (14) electrically separated over the slot (20), when the antenna structure is operating in the frequency band.
According to the fourth aspect of the present invention, there is provided an antenna structure (2) comprising a first antenna (70, 80) and a second antenna (40), each antenna having a radiating element, a feed line and a grounding strip coupling to the radiating element to a ground plane, wherein one of the first and second antennas is used for transmission and the other is used for reception. The antenna structure (2) is characterized in that
the radiating element (78, 88, 90) has a slot (76, 86) provided thereon for effectively separating the feed line (72, 82) and the grounding strip (74, 84) of the first antenna (70, 80) by a distance substantially equal to one half wavelength of a resonant frequency of the radiating element (78, 88, 90) of the first antenna.
Preferably, the slot has a length substantially equal to a quarter-wavelength of the resonant frequency.
Preferably, the first antenna is a slot antenna and the second antenna is a planar inverted-F antenna.
Advantageously, the first antenna (80) is a multiple-band antenna operating in at least a first frequency band and a second frequency band different from the first frequency band, the first antenna further having a further radiating element coupled to the radiating element, and wherein the resonant frequency of the radiating element of the first antenna falls within the first frequency band, and the further radiating element has a resonant frequency within the second frequency band.
Advantageously, the radiating element of the second antenna has a resonant frequency within the first frequency band.
According to the fifth aspect of the present invention, there is provided a method of improving isolation in antenna structure (2), wherein the antenna structure comprises a first antenna (70, 80) and a second antenna (40), each antenna having a radiating element, a feed line and a grounding strip coupling to the radiating element to a ground plane, wherein one of the first and second antennas is used for transmission and the other is used for reception. The method is characterized by
providing a slot (76, 86) on the radiating element (78, 88, 90) for effectively separating the feed line (72, 82) and the grounding strip (74, 84) of the first antenna (70, 80) by a distance substantially equal to one half wavelength of a resonant frequency of the radiating element (78, 88, 90) of the first antenna.
Preferably, the slot has a length substantially equal to one quarter-wavelength of the resonant frequency.
The present invention will become apparent by reading the description taken in conjunction with FIGS. 1 to 5b.